1. Field of the Invention
The present invention relates to a welding apparatus for welding workpieces in a butt welding. More particularly, it relates to a welding apparatus for precisely and speedy setting each projecting degree of each workpiece required in the butt welding.
2. Description of the Prior Arts
FIG. 1 shows the conventional welding apparatus.
In FIG. 1, the reference (1) designates a movable frame which can be horizontally shifted to a stationary frame (2); (3a) and (3b) respectively designate a movable side upper electrode table and a movable side lower electrode table which are fitted on the movable frame (1). The upper electrode table (3a) can be vertically shifted by a movable side pressing device (6) whereas the lower electrode table (3b) is mounted on the movable frame (1). Thus, the workpiece (8) can be clamped between the upper electrode table (3a) and the lower electrode table (3b).
On the other hand, the mutual relations of a stationary side upper electrode table (4a), a stationary side lower electrode table (4b), a stationary side pressing device (7) and a workpiece (9) are the same with those of the parts in the movable frame (1) as described above.
Thus, the workpieces (8), (9) are respectively clamped by the electrode tables (3a), (3b) and (4a), (4b) to shift the workpieces (8), (9) to the butting direction so as to butt the edges thereof and a current is fed through the electrode table (3b), (4b) to the workpieces (8), (9) to attain the welding operation.
The most important feature for attaining excellent butt welding operation is to set the current passing distance for the workpieces (8), (9) i.e. the distance between each electrode (3b) and the end of each workpiece (8) and the distance between each electrode (4b) and the end of each workpiece (9) (See FIG. 1) should be set in suitable distance.
This distance is usually referred to as a projecting degree and suitable distance is selected depending upon the kind and size e.g. thickness of the workpiece. Thus, in the butt welding operation, it is necessary to set the optimum projecting degree depending upon the kind and size of the workpiece before feeding the current under butting the workpieces.
In FIG. 1, the reference (5) is a step gauge bar for setting the optimum projecting degrees and the step gauge bar (5) is disposed between the movable side electrode tables (3a), (3b) and the stationary side electrode tables (4a), (4b) and is vertically movable so as to contact the ends of the workpieces (8), (9) to the surfaces of the suitable step of the step gauge bar (5), whereby it sets the optimum projecting degrees of the workpieces (8), (9) under projecting from the side surfaces of the electrode tables (3a), (3b), (4a) and (4b).
The thickness of the step gauge bar (5) is varied to be several thickness in steps and the vertical position of the step gauge bar (5) is adjusted so as to contact the ends of the workpieces with the step of the step gauge bar corresponding to the workpiece.
When the movable frame (1) is shifted to the direction for the butt welding of the workpieces (8), (9), the step gauge bar (5) is removed so as to prevent the trouble.
It is possible to set the optimum projecting degree by the apparatus of FIG. 1. However, in accordance with the conventional apparatus, many steps of the step gauge bar (5) are required for corresponding the projecting degree to the optimum one in wide ranges of kinds of materials and sizes of the workpieces, whereby the disadvantages of complicated operations for controlling the step gauge bar such as setting and removing operations have been found.
In order to overcome the disadvantages, the conventional apparatus shown in FIG. 2 has been proposed.
The apparatus shown in FIG. 2 has the novel feature that shear units (10a), (10b), auxiliary clamps (11a), (11b) and (12a), (12b) and auxiliary clamp delivery devices (13), (14) are employed instead of the step gauge bar (5) which is considerably different from the feature of the embodiment shown in FIG. 1.
In the apparatus of FIG. 1, the projecting degree of the workpiece is set by the step gauge bar (5) whereas in the apparatus of FIG. 2, the edges of the workpieces (8), (9) projected from the electrode tables (3a), (3b) and (4a), (4b) are sheared off at the specific positions by the shear units (10a), (10b) and the workpiece (8) is fixed by the auxiliary clamps (11a), (11b) and the auxiliary clamps (11a), (11b) are shifted to approach or to depart by the movable side auxiliary clamp delivery device (13) to set the optimum projecting degree of the workpiece (8). When the workpiece (8) is shifted for setting the projecting degree, the electrode tables (3a), (3b) should be opened. On the other hand, the projecting degree of the workpiece (9) in the stationary frame (2) is set by employing the auxiliary clamps (12a), (12b), and the stationary side auxiliary clamp delivery device (14) in the same manner with those of the movable side at the same time.
When the movable frame (1) is shifted to the butting direction, for the butt welding of the workpieces (8), (9), the shear units (10a), (10b) can be removed to prevent the trouble.
In accordance with the apparatus of FIG. 2, there is no disadvantage of the apparatus of FIG. 1 since a step gauge bar is not employed. Accordingly, it is possible to carry out the welding of various workpieces in wide ranges of kinds of materials and sizes.
However, the apparatus of FIG. 2 has the following disadvantages.
As well-known, considerably high force caused in the butt welding operation is received by the electrode tables whereby the electrode tables should be large in size and the pressing devices should have considerably high power whereby a relatively long time is required for shifting the electrode table.
However, in the apparatus of FIG. 2, the workpieces (8), (9) are clamped by the electrode tables (3a), (3b) and (4a), (4b) for shearing the workpieces and then, the workpieces are released when the auxiliary clamps (11a), (11b) and (12a), (12b) are shifted for setting the projecting degree and then, the workpieces are clamped again for welding them whereby a long time is required for the welding operation.